Added workaround for custom headers not being set correctly.

URestemplateApp.pas

@@ -83,7 +83,7 @@ implementation
 
 uses
   strutils, crt, UCRTHelper, fpjson, DOM, XMLRead, XMLWrite, vinfo,
-  IdCompressorZLib;
+  IdCompressorZLib, IdHeaderList, IdGlobalProtocols;
 
 type
   TContentType = (ctOther, ctJSON, ctXML);
@@ -103,9 +103,30 @@ end;
 { TRestRequest }
 
 procedure TRestRequest.Prepare;
+var
+  originalHeaders: TIdHeaderList;
+  i: Integer;
 begin
   //Parse RawHeaders, since they have precendence and should not be overridden!
   ProcessHeaders;
+
+  //SetHeaders clears RawHeaders and therefore discards our custom headers.
+  //We work around that by remembering what is set.
+  originalHeaders := TIdHeaderList.Create(QuoteHTTP);
+  try
+    originalHeaders.Assign(FRawHeaders);
+    //Now we call SetHeaders to be able to find out what was custom and what
+    //was known.
+    SetHeaders;
+
+    for i := 0 to originalHeaders.Count - 1 do
+    begin
+      if FRawHeaders.IndexOfName(originalHeaders.Names[i]) < 0 then
+        FCustomHeaders.Add(originalHeaders.Strings[i]);
+    end;
+  finally
+    originalHeaders.Free;
+  end;
 end;
 
 { TRestHTTP }
@@ -390,6 +411,10 @@ begin
     FRequest.Prepare;
     FHttp.Request := FRequest;
     FHttp.HTTPOptions := FHttp.HTTPOptions + [hoNoProtocolErrorException];
+
+    // Workaround for CustomHeaders not being assigned :-/
+    FHttp.Request.CustomHeaders.AddStrings(FRequest.CustomHeaders);
+
     if SameText('POST', FMethod) and (FFormFields.Count > 0) then
       FHttp.Post(AURL, FFormFields, response)
     else